This invention relates to general voltage drop compensating type transformer power supply systems with Turn-On control feature to prevent accidental burnout of the supplied load equipment. More specifically stated, it relates to a novel Turn-On control system for voltage drop compensators to provide full protection against overcompensation upon restoration of the power supply voltage immediately following a Utility blackout.
There are various commercially available automatic voltage drop compensators being equipped with automatic controls sensing the Utility's line voltage fluctuations. Normally the control units comprise a reference circuit generating a DC signal remaining constant regardless of the incoming line voltage variations. Further it consists of a feed-back circuit to produce a feedback signal being continuously compared with the magnitude of the reference signal. Thus at any time-moment their differences resulting in a corresponding error signal-positive or negative- to provide a proportionate corrective control on the voltage drop compensator to reestablish the required constant operating voltage on the load.
Generally the maximum voltage correction capacity of all voltage drop compensators amounts to +20% of the rated Utility service line voltage. Consequently following a slow blackout, at the time-moment of power return, the voltage drop compensator's setting will unavoidably be at its highest corrective output voltage, which will subsequently result in an excessive over-voltage compensation. More particularly in Computer Voltage Stabilizer applications, such over-voltage compensation will cause diastrous damaging effect on the computer equipment and possibly may even destroy it.
For series transformer type voltage drop compensators equipped with variable voltage transformer, the turn-on control system comprises a contactor-coil with a plurality of operatively interlocking switching contacts to perform switching operations in a predetermined succession consisting of disconnecting and subsequent resetting the variable voltage transformer to its lowest corrective position with following reconnection to resume automatic voltage corrective operation.
Further structural feature of the turn-on control system provides a time-delay action to allow the controlling motor device sufficient time to reach a full stop before the reversal of the controlling action shall take place.
More specifically stated, this invention relates to a novel Turn-On control system to safely prevent the occurrence of such damaging effects noted above. In accordance with the invention the control system shall be activated at the moment of blackout or power feeding interruption by applying the following method:
In a predetermined sequential order, at first the compensator's control device shall be made inoperative, then it shall be reset to zero position or apparatus lowest voltage so that after restoration of normal power it becomes again operative, whereby no over-voltage can occur.